Humidification of a pressurized flow of breathable gas

ABSTRACT

A system (10) configured to facilitate humidification of a pressurized flow of breathable gas delivered to a subject (12) comprises a pressure generator (14), a nebulizer (16), a heater (38), one or more hardware processors (22), and/or other components. The pressure generator is configured to generate a pressurized flow of breathable gas for delivery to an airway (24) within a trachea of the subject. The nebulizer is configured to provide fluid droplets (54) to the breathable gas. The heater is configured to heat a volume of the breathable gas before the droplets are supplied to the breathable gas. The breathable gas received by the subject exhibits a target temperature and humidity level at short distance d from the nebulizer due to one or more of a number of the droplets, an average size of the droplets, a gas flow rate, and/or an amount of heating power.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the priority benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 62/433,875 filed on Dec. 14,2016, the contents of which are herein incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure pertains to systems and methods for facilitatinghumidification of a pressurized flow of breathable gas delivered to asubject.

2. Description of the Related Art

It is well known to ventilate a subject's (e.g., a patient's) airway tosupply a pressurized flow of breathable gas to the subject.Humidification technologies for ventilation have been developed. Onekind of humidification device is a so-called “heated humidifier” wherethe flow of breathable gas is conducted over a heated water reservoir.In the application of humidification of air for ventilated subjects(e.g., patients), these devices are targeted to deliver an air flow ofat least 33° C. temperature at a relative humidity close to 100%. Thedisadvantage of these devices is the high heating power (˜60-70 W)needed to heat the water reservoir and to evaporate the water vapor.Furthermore, they are bulky and pose a security risk, since they mightbe a source of thermal injury to human skin.

So-called “personal humidifiers” are devices within the air supply froma ventilator (e.g., a pressure generator) that are located close to thetracheal cannula of the subject. These devices have the advantage thatthey are light-weight and have low power consumption (˜3-5 W). Thesenebulizers may inject droplets having, for example, ˜5 μm diameters at atarget rate of ˜33 mg/L into the air stream during inhalation to raisethe humidity of the air delivered to the subject. One example of anebulizer head for use in a “personal humidifier” would be a “vibratingmesh nebulizer” manufactured by Aerogen, Inc.

When water or saline droplets of ˜5 μm diameter are injected into theinhaled air at a rate of ˜33 mg/L, the temperature of the mist will dropdue to partial evaporation of the droplets. Due to fast energy exchangewith the air molecules, the air/droplet mist entering the subject'sairways will have a temperature several degrees Celsius below theoriginal temperature of the air but at a relative humidity of 100%. Sucha comparatively cold and therefore dry air inflow (100% relativehumidity (RH) at the lower temperature corresponds to a lower absolutewater vapor concentration than 100% RH at room temperature) may induce amarked heat and water vapor flow from the skin of the subject's uppertrachea into the inhaled airflow. The skin of the subject's uppertrachea may thus be cooled and dried out which will lead to anuncomfortable feeling and an increased risk of infection and ciliarydysfunctionality. The droplets might be not able to prevent the dryingout of the tracheal skin, because only a small fraction (e.g. 10-30%) ofthe droplets will be deposited at the trachea surface.

As an example, consider a scenario with an air inflow of 30 liters perminute (LPM) with an air temperature (T_(air)) equal to 20° C. with 64%relative humidity.) When water or saline droplets of ˜5 μm diameter areinjected into the inhaled air at a rate of ˜33 mg/L, the temperature ofthis mist will drop within ˜5 ms by ˜4.4° C. due to partial evaporationof the droplets. If the air stream from the ventilator has a temperatureof 20° C. and a water vapor concentration of 11 mg/L (which equals 64%relative humidity), then the air/droplet mist entering the patient'sairways will thus have a temperature of 15.6° C. at a relative humidityof 100% (i.e., a water vapor concentration of 13.4 mg/L).

Furthermore, a large fraction (up to 90%) of the droplets of ∥5 μmdiameter will be lost from the air stream by collision with the walls ofthe bend of the tracheal cannula. This mechanism is known in theliterature as “impaction.” Impaction will lead to a liquid film coveringthe lower surface of the tracheal cannula, and gravity will help to formlarge (˜1 mm diameter) droplets of liquid at the lower rim of thecannula from which those large droplets may drop into the trachea andthe lower airways (e.g., bronchi and bronchioles). Also this effectmight lead to an uncomfortable feeling and an increased risk ofinfection.

Therefore, a device is missing in the art that combines the advantagesof a “personal humidifier” (light-weight, low power) and an adequatetemperature and humidity level at the subject interface without the needof high power consumption, which would make a mobile applicationimpossible (e.g., for a patient in a wheelchair).

SUMMARY OF THE INVENTION

Accordingly, one or more aspects of the present disclosure relate to asystem configured to facilitate humidification of a pressurized flow ofbreathable gas delivered to a subject. The system comprises a pressuregenerator, a nebulizer, a heater, one or more hardware processors,and/or other components. The pressure generator is configured togenerate a pressurized flow of breathable gas for delivery to an airwaywithin a trachea of the subject. The nebulizer is configured to providefluid droplets to the breathable gas. The heater is configured to causethe pressure generator to deliver a flow of breathable gas to thesubject; cause the nebulizer to provide fluid droplets to the breathablegas; and cause the heater to heat a volume of the breathable gas beforefluid droplets are supplied to the breathable gas. The breathable gasreceived by the subject exhibits a target temperature and humidity levelat short distance d from the nebulizer due to one or more of a number ofthe droplets, an average size of the droplets, a gas flow rate, and/oran amount of heating power.

Yet another aspect of the present disclosure relates to a method forfacilitating humidification of a pressurized flow of breathable gasdelivered to a subject with a system. The system comprises a pressuregenerator, a nebulizer, a heater, and one or more hardware processors.The method comprises generating, with the pressure generator, apressurized flow of breathable gas for delivery to an airway within atrachea of the subject; providing fluid droplets, with the nebulizer, tothe pressurized flow of breathable gas; and heating, with the heater, avolume of the breathable gas before moisture is supplied to thebreathable gas. The breathable gas received by the subject exhibits atarget temperature and humidity level at short distance d from thenebulizer due to one or more of a number of the droplets, an averagesize of the droplets, a gas flow rate, and/or an amount of heatingpower.

Still another aspect of the present disclosure relates to a system forfacilitating humidification of a pressurized flow of breathable gasdelivered to a subject. The system comprises means for generating apressurized flow of breathable gas for delivery to an airway within atrachea of the subject; means for providing fluid droplets to thepressurized flow of breathable gas; and means for heating a volume ofthe breathable gas before moisture is supplied to the breathable gas.The breathable gas received by the subject exhibits a target temperatureand humidity level at short distance d from the means for providingfluid droplets due to one or more of a number of the droplets, anaverage size of the droplets, a gas flow rate, and/or an amount ofheating power.

These and other objects, features, and characteristics of the presentdisclosure, as well as the methods of operation and functions of therelated elements of structure and the combination of parts and economiesof manufacture, will become more apparent upon consideration of thefollowing description and the appended claims with reference to theaccompanying drawings, all of which form a part of this specification,wherein like reference numerals designate corresponding parts in thevarious figures. It is to be expressly understood, however, that thedrawings are for the purpose of illustration and description only andare not intended as a definition of the limits of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a system configured to facilitate humidification of apressurized flow of breathable gas delivered to a subject, in accordancewith one or more embodiments;

FIG. 2 illustrates a view of a graphical user interface presented to thesubject, in accordance with one or more embodiments;

FIG. 3 illustrates a second view of the graphical user interface, inaccordance with one or more embodiments;

FIG. 4 illustrates a system configured to facilitate humidification of apressurized flow of breathable gas delivered to a subject, in accordancewith one or more embodiments;

FIG. 5 illustrates a simulation model of a personal nebulizer, inaccordance with one or more embodiments;

FIG. 6 illustrates a simulation model of a personal nebulizer, inaccordance with one or more embodiments;

FIG. 7 illustrates a simulation model of a personal nebulizer, inaccordance with one or more embodiments; and

FIG. 8 illustrates a method for facilitating the addition of droplets toa pressurized flow of breathable gas delivered to a subject, inaccordance with one or more embodiments.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

As used herein, the singular form of “a”, “an”, and “the” include pluralreferences unless the context clearly dictates otherwise. As usedherein, the statement that two or more parts or components are “coupled”shall mean that the parts are joined or operate together either directlyor indirectly, i.e., through one or more intermediate parts orcomponents, so long as a link occurs. As used herein, “directly coupled”means that two elements are directly in contact with each other. As usedherein, “fixedly coupled” or “fixed” means that two components arecoupled so as to move as one while maintaining a constant orientationrelative to each other.

As used herein, the word “unitary” means a component is created as asingle piece or unit. That is, a component that includes pieces that arecreated separately and then coupled together as a unit is not a“unitary” component or body. As employed herein, the statement that twoor more parts or components “engage” one another shall mean that theparts exert a force against one another either directly or through oneor more intermediate parts or components. As employed herein, the term“number” shall mean one or an integer greater than one (i.e., aplurality).

Directional phrases used herein, such as, for example and withoutlimitation, top, bottom, left, right, upper, lower, front, back, andderivatives thereof, relate to the orientation of the elements shown inthe drawings and are not limiting upon the claims unless expresslyrecited therein.

FIG. 1 illustrates a system 10 configured to facilitate humidificationof a pressurized flow of breathable gas delivered to a subject 12. Insome embodiments, the present technology can be applied as an optimized“personal humidifier” for (ventilated) subjects breathing via atracheostoma. In some embodiments, system 10 includes one or more of apressure generator 14, a nebulizer 16, a subject interface 24, asensor(s) 18, a user interface 20, a processor 22, electronic storage50, and/or other components. A fast air heater, such as heater 38 ofFIG. 4, may also be provided. In some embodiments, heater 38 may belocated between pressure generator 14 and a droplet injector, such asnebulizer 16. Heater 38 may also be located in apposition with nebulizer16, in some embodiments. In some embodiments, a fast temperature sensor,such as a sensor 18, may be located at an entrance to a subject (such asa conduit 28) of the tracheal cannula, a mask, etc.

In some embodiments, a personal nebulizer may include one or more of thetracheal cannula, conduit 28, subject interface 24, interface appliance30, and/or other elements. In some embodiments, heater 38 may be withinconduit 28. In other embodiments, conduit 28 may pass through heater 38.In some embodiments, a time-dependent air heating power is modulated andproportional to a flow of air (flow of breathable gas), wherein there isno heating during exhalation. In some embodiments, heater 38 includes afast heating element with a time constant of less than 1 second tomaintain the temperature of the flow of breathable gas constant duringinhalation (because gas flow varies during inhalation) and to ensuresafety (i.e., a fast switch-off is made if nebulizer 16 is failing. Allother suitable time constants are contemplated.

System 10 is configured to provide a humidity- andtemperature-controlled pressurized flow of breathable gas to subject 12.In some embodiments, instead of cold room air, a supply warm air isprovided to nebulizer 16, which is generating a mist of water. The airflow for inspiration coming from the ventilator, such as pressuregenerator 14, is passed through heater 38 where a time-dependent heatingpower P(t) is transferred to the breathing gas. The final gas/mistmixture temperature, needed heating power, and also needed minimumdistance of the nebulizer to the “trach” are determined by the gas flowrate, water droplet amount and size, and start gas temperature. In someembodiments, as discussed herein, this minimum distance ranges fromabout 1 cm to about 30 cm. Advantageously, the mixture will have 100%relative humidity in some embodiments.

This air temperature and humidity (close to the situation found whenusing a “conventional” vapor humidifier, which is based on saturatingthe inhaled air with water vapor above a heated water reservoir) causesless heat and water vapor loss from the subject's upper trachea withrespect to previous droplet nebulizers.

In some embodiments, after establishing this air/droplet mistequilibrium, droplets 54 are partially evaporated and thus have areduced diameter. Advantageously, those droplets 54 (with reduceddiameters) have a much higher probability of reaching the airways ofsubject 12 without hitting the walls of the tracheal cannula bend. Inputparameters can also be chosen to influence and/or optimize the size ofdroplets 54 remaining in the air/droplet mist mixture. That is, thedroplet size is adapted to the geometry of the used “trach tube,” forexample.

More specifically, in some embodiments, instead of cold room air asupply warm air of ˜48° C. is provide to nebulizer 16 (the “personalhumidifier”), which is generating a mist of water droplets of ˜5 μmdiameter at a rate of ˜16 mg/L (e.g., at about half the target rate of aprior droplet nebulizer). Numerical simulations show that theequilibrium composition of the air/droplet mist entering subject's 12airways will then have a temperature of 25° C. at a relative humidity of100% (corresponding to a water vapor concentration of 23.4 mg/L) andthat this equilibrium will be reached within short time (˜10 ms) or,correspondingly, within a short distance (less than 7.5 cm when takingthe maximum gas velocity on the axis during inhalation as 7.5 m/s). Thisair temperature and humidity (close to the situation found when using a“conventional” vapor humidifier which is based on saturating the inhaledair with water vapor above a heated water reservoir) causes less heatand water vapor loss from subject's 12 upper trachea with respect to theprior droplet nebulizers.

In some embodiments, a “trach tube,” or tracheal cannula (conduit 28)has an inner diameter of 8 mm and a curvature radius of 20 mm. However,all other inner diameters and curvature radii are contemplated. Afterestablishing the air/droplet mist equilibrium, the droplets arepartially evaporated and thus have a reduced diameter (reduced from 5 μmto 3 μm) because the mass rate output of the nebulizer is reduced insome embodiments (from 33 mg/L to 16 mg/L). At 33 mg/L droplets 54 wouldhave a diameter of 4.3 μm after establishing equilibrium. As mentioned,those droplets 54 having a reduced diameter (reduced from 5 μm to 3 μm)have a much higher probability of reaching the airways without hittingthe walls of the tracheal cannula bend. (Assuming a peak volume flow of70 L/min during inhalation it is simulated that 62% of the 5 μm diameterdroplets would hit the trach walls, whereas this number would be only10% for the 3 μm diameter droplets). If considerably fewer droplets arehitting the tracheal cannula's walls, then the risk of forming largedrops of water at the lower rim of the trach that would drop into thelower airways is greatly reduced.

In some embodiments, the air flow for inspiration coming from pressuregenerator 14 is passed through heater 38 where a time-dependent heatingpower P(t) is transferred to the breathable gas. Ideally, the heatingpower P(t) should be proportional to the gas flow Φ(t). To reach thedesired temperature of 48° C., a heating energy density of about 36 J/Lis required. Assuming a tidal volume of 0.5 L and a duration of 1 s forthe inspiration phase, an average heating power of 36 J/L*0.5 L/1 s=18 Wcan be estimated.

As mentioned herein, for security and/or safety reasons, a fasttemperature sensor at the entrance of the tracheal cannula (or otherentrance to the subject) is added to trigger switch-off of the airheater if the nebulizer fails to produce droplets. The mass rate of thenebulizer is adjusted (i.e., reduced) from ˜33 mg/L to ˜16 mg/L so thatdroplet 54 diameter is reduced (from 5 μm to 3 μm) during theequilibration phase. It should be noted that the numbers mentionedwithin this disclosure are merely exemplary and not intended to belimiting. All other suitable numbers and values are contemplated to beused with the present technology in various embodiments.

In some embodiments, system 10 is configured to provide a humiditycontrolled pressurized flow of breathable gas to subject 12 according toa predetermined pressure support therapy regime. System 10 is configuredto generate output signals and/or determine various parameters relatedto the pressurized flow of breathable gas. System 10 is configured toreceive feedback from subject 12 related to a comfort level of subject12 during therapy. System 10 is configured to automatically adjust thepressurized flow of breathable gas and/or the predetermined therapyregime, provide feedback to subject 12, and/or prompt subject 12 to makemanual adjustments based on the output signals, the determinedparameters, the feedback from subject 12, and/or other information. Thefeedback provided to subject 12 may include, for example, arecommendation to try a different therapy regime and/or alternatetherapy devices, and/or other feedback. The manual adjustments may be,for example, manual adjustments to one or more components of system 10,manual adjustments to the ambient environment, and/or other manualadjustments. System 10 is configured to simplify adjustments to humiditycontrol and/or pressure support therapy that enhance the comfort levelof subject 12 during therapy.

For example, system 10 may determine, obtain, and/or receive informationrelated to an ambient temperature, a relative ambient humidity, leak,the humidification method, humidification method set points (e.g., atarget humidity level, etc.), a subject interface (e.g., conduit)temperature, water usage (e.g., per hour and/or per session), and/orother parameters. System 10 may receive feedback from subject 12 thatincludes information related to an inhaled air temperature rating (e.g.,0 being too cold, 10 being too hot), an inhaled air moisture rating(e.g., 0 being too dry, 10 being too wet), whether or not subject 12 hasexperienced tube rainout, whether or not subject 12 has experienced maskrainout, and/or other information. System 10 is configured to analyzethe parameter information and the feedback from subject 12 and make anautomatic adjustment to the pressure support therapy regime, providefeedback to subject 12, prompt subject 12 and/or other users to make amanual adjustment to system 10 and/or the ambient environment, and/ortake other actions. Other users may include a doctor, a caregiver,and/or other users. System 10 reduces the burden on subject 12 todetermine which adjustments to make to increase his comfort level duringtherapy.

As illustrated in FIG. 1, pressure generator 14 is configured togenerate a pressurized flow of breathable gas for delivery to an airwayof subject 12. Pressure generator 14 is also configured to facilitatehumidification of the pressurized flow of breathable gas delivered tosubject 12. Pressure generator 14 may control one or more parameters ofthe flow of gas (e.g., flow rate, pressure, volume, temperature, gascomposition, etc.) for therapeutic purposes, and/or for other purposes.By way of a non-limiting example, pressure generator 14 may beconfigured to control the flow rate and/or pressure of the flow of gasto provide pressure support to the airway of subject 12.

Pressure generator 14 receives a flow of gas from a gas source, such asthe ambient atmosphere, as indicated by arrow A in FIG. 1 and elevatesthe pressure of that gas for delivery to the airway of subject 12.Pressure generator 14 is any device, such as, for example, a pump,blower, piston, or bellows, that is capable of elevating the pressure ofthe received gas for delivery to subject 12. The present disclosure alsocontemplates that gas other than ambient atmospheric air may beintroduced into system 10 for delivery to subject 12. In suchembodiments, a pressurized canister or tank of gas containing air,oxygen, and/or another gas may supply the intake of pressure generator14. In some embodiments, pressure generator 14 need not be provided, butinstead the gas may be pressurized by the pressure of the canisterand/or tank of pressurized gas itself.

In some embodiments, pressure generator 14 is a blower that is driven ata substantially constant speed during the course of the pressure supporttreatment to provide the pressurized flow of breathable gas with asubstantially constant elevated pressure and/or flow rate. Pressuregenerator 14 may comprise a valve for controlling the pressure/flow ofgas. The present disclosure also contemplates controlling the operatingspeed of the blower, either alone or in combination with such a valve,to control the pressure/flow of gas provided to subject 24.

The pressurized flow of breathable gas is delivered to the airway ofsubject 12 from pressure generator 14 and/or nebulizer 16 via subjectinterface 24. Subject interface 24 is configured to communicate thepressurized flow of breathable gas generated by pressure generator 14and/or humidified by nebulizer 16 to the airway of subject 12. As such,subject interface 24 comprises one or more conduits 28, an interfaceappliance 30, and/or other components. Conduits 28 are configured toconvey the pressurized flow of gas to interface appliance 30. Interfaceappliance 30 is configured to deliver the flow of gas to the airway ofsubject 12. In some embodiments, interface appliance 30 is non-invasive.As such, interface appliance 30 non-invasively engages subject 12.Non-invasive engagement comprises removably engaging an area (or areas)surrounding one or more external orifices of the airway of subject 12(e.g., nostrils and/or mouth) to communicate gas between the airway ofsubject 12 and interface appliance 30. Some examples of non-invasiveinterface appliance 30 may comprise, for example, a tracheal cannula, anasal cannula, a nasal mask, a nasal/oral mask, a full face mask, atotal face mask, or other interface appliances that communicate a flowof gas with an airway of a subject. The present disclosure is notlimited to these examples, and contemplates delivery of the flow of gasto subject 12 using any interface appliance.

Although subject interface 24 is illustrated in FIG. 1 as asingle-limbed circuit for the delivery of the flow of gas to the airwayof subject 12, this is not intended to be limiting. The scope of thisdisclosure comprises double-limbed circuits having a first limbconfigured to provide the flow of gas to the airway of subject 12, and asecond limb configured to selectively exhaust gas from subject interface24 (e.g., to exhaust exhaled gases).

Sensor 18 is configured to generate output signals conveying informationrelated to one or more parameters of the pressurized flow of breathablegas. Information related to one or more parameters of the pressurizedflow of breathable gas may include information related to a flow rate, avolume, a pressure, humidity, temperature, acceleration, velocity,and/or other gas parameters; breathing parameters related to therespiration of subject 12 such as a tidal volume, a timing (e.g.,beginning and/or end of inhalation, beginning and/or end of exhalation,etc.), a respiration rate, a duration (e.g., of inhalation, ofexhalation, of a single breathing cycle, etc.), respiration frequency,and/or other breathing parameters; parameters related to the operationof pressure generator 14, nebulizer 16, and/or other components ofsystem 10; parameters related to the ambient environment, and/or otherinformation. Sensor 18 may comprise one or more sensors that measuresuch parameters directly (e.g., through communication with thepressurized flow of breathable gas in conduit 28). Sensor 18 maycomprise one or more sensors that generate output signals related to thepressurized flow of breathable gas indirectly. For example, sensor 18may comprise one or more sensors configured to generate an output basedon an operating parameter of pressure generator 14, nebulizer 16 (e.g.,a current drawn, voltage, and/or other operation/operating parameters),and/or other sensors.

Sensor 18 may include pressure sensors, flow rate sensors, volumesensors, humidity sensors, liquid level sensors, usage time sensors,temperature sensors, external sensors 19, and/or other sensors. Externalsensors 19 may include, for example, altitude sensors, homeheating/cooling mode/settings sensors (e.g., configured to generateoutput signals conveying information related to home HVAC mode,settings, mode cycle, etc.), room ambient conditions sensors, homeexterior ambient conditions sensors, and/or other sensors. Sensors 18and/or 19 may include a plurality of individual sensors located atvarious locations throughout system 10, in the immediate sleeping area,in the home and/or positioned to generate information about conditionsexterior to the home (e.g., environmental conditions measured by thesystem and/or retrieved from some other system or database).

FIG. 1 illustrates four different locations for individual sensors 18and one location of external sensors 19. This is not intended to belimiting. System 10 may include any number of sensors 18 and/or 19located anywhere within system 10 and/or in proximity to system 10provided system 10 functions as described herein. For example, sensor 18may include one or more of pressure, flow rate, humidity, temperature,and/or other sensors in communication with the pressurized flow ofbreathable gas in conduit 28. Sensor 18 may be and/or include atransducer configured to detect acoustic waves transmitted throughsubject interface 24. These acoustic waves may convey informationrelated to respiratory effort of subject 12, and/or the noise generatedby subject 12 during respiration (e.g., during snoring). Sensor 18 maybe and/or include liquid level sensors configured to generate one ormore output signals conveying information related to a current liquidlevel 23 in nebulizer 16.

In this example, sensor 18 may be and/or include one or more of a floatswitch, a pressure sensor, an ultrasonic sensor, a heat capacity basedsensor, and/or other liquid level sensors. Sensor 18 may be and/orinclude usage time sensors configured to generate one or more outputsignals conveying information related to one or more usage timeparameters. The one or more usage time parameters may compriseparameters related to the total time subject 12 spends connected tosystem 10 during a usage session, and/or the time subject 12 is asleepwhile connected to system 10 during a usage session. Sensor 18 mayinclude one or more subject interface temperature sensors configured togenerate one or more output signals conveying information related to thetemperature of one or more components of subject interface 24. Sensor 18may include one or more environmental sensors configured to generateoutput signals related to conditions (e.g., temperature, humidity) ofthe ambient environment around system 10. At the top of liquid level 23there is a mesh 52 through which droplets 54 pass.

User interface 20 is configured to receive entry and/or selection offeedback information from subject 12 and/or other users indicating aninitial comfort level with the pressurized flow of breathable gas. Afteran automatic adjustment to the pressurized flow of breathable gas(described below), user interface 20 is configured to receive entryand/or selection of additional feedback information from subject 12indicating an adjusted comfort level. User interface 20 is configured toprovide an interface between system 10 and subject 12 and/or other users(e.g., a doctor, care-giver, etc.) through which subject 12 may provideinformation to and receive information from system 10. This enablesdata, cues, results, and/or instructions and any other communicableitems, collectively referred to as “information,” to be communicatedbetween subject 12 and one or more of pressure generator 14, electronicstorage 50, processor 22, and/or other components of system 10. Examplesof interface devices suitable for inclusion in user interface 20comprise a keypad, buttons, switches, a keyboard, knobs, levers, adisplay screen, a touch screen, speakers, a microphone, an indicatorlight, an audible alarm, a printer, a tactile feedback device, and/orother interface devices.

It is to be understood that other communication techniques, eitherhard-wired or wireless, are also contemplated by the present disclosureas user interface 20. For example, the present disclosure contemplatesthat user interface 20 may be integrated with a removable storageinterface provided by electronic storage 50. In this example,information may be loaded into system 10 from removable storage (e.g., asmart card, a flash drive, a removable disk, etc.) that enables theuser(s) to customize the implementation of system 10. Other exemplaryinput devices and techniques adapted for use with system 10 as userinterface 20 comprise, but are not limited to, an RS-232 port, RF link,an IR link, modem (telephone, cable or other). In short, any techniquefor communicating information with system 10 is contemplated by thepresent disclosure as user interface 20.

In some embodiments, user interface 20 comprises a plurality of separateinterfaces. In some embodiments, user interface 20 comprises at leastone interface that is provided integrally with pressure generator 14. Insome embodiments, user interface 20 includes one or more of a userinterface that is integral with pressure generator 14 and/or a graphicaluser interface presented to subject 12 via a client computing device(not shown in FIG. 1). For example, user interface 20 may be and/orinclude a graphical user interface that is presented to subject 12 on asmartphone and/or other computing device associated with subject 12.This may allow subject 12 to provide feedback to system 10, receivefeedback from system 10, and/or receive a prompt to make a manualadjustment (for example) during therapy and/or at other times whilesubject 12 is not in immediate proximity to pressure generator 14 and/ornebulizer 16, for example.

Processor 22 is configured to provide information processingcapabilities in system 10. As such, processor 22 may comprise one ormore of a digital processor, an analog processor, a digital circuitdesigned to process information, an analog circuit designed to processinformation, a state machine, and/or other mechanisms for electronicallyprocessing information. Although processor 22 is shown in FIG. 1 as asingle entity, this is for illustrative purposes only. In someembodiments, processor 22 may comprise a plurality of processing units.These processing units may be physically located within the same device(e.g., pressure generator 14, nebulizer 16, a client computing device),or processor 22 may

As shown in FIG. 1, processor 22 is configured to execute one or morecomputer program components. The one or more computer program componentsmay include one or more of a flow delivery component 40, a nebulizercomponent 42, a heater component 44, and/or other components. Processor22 may be configured to execute components 40, 42, and/or 44 bysoftware; hardware; firmware; some combination of software, hardware,and/or firmware; and/or other mechanisms for configuring processingcapabilities on processor 22.

It should be appreciated that although components 40, 42, and 44 areillustrated in FIG. 1 as being co-located within a single processingunit, in embodiments in which processor 22 includes multiple processingunits, one or more of components 40, 42, and/or 44 may be locatedremotely from the other components. The description of the functionalityprovided by the different components 40, 42, and/or 44 described belowis for illustrative purposes, and is not intended to be limiting, as anyof components 40, 42, and/or 44 may provide more or less functionalitythan is described. For example, one or more of components 40, 42, and/or44 may be eliminated, and some or all of its functionality may beprovided by other components 40, 42 and/or 44. As another example,processor 22 may be configured to execute one or more additionalcomponents that may perform some or all of the functionality attributedbelow to one of components 40, 42, and/or 44.

In some embodiments, flow delivery component 40 is configured to causepressure generator 14 to deliver a flow of breathable gas to thesubject. Nebulizer component 42 is configured to cause nebulizer 16 toprovide moisture to the breathable gas. Heater component 44 isconfigured to cause heater 38 to heat a volume of the breathable gasbefore moisture and/or droplets are supplied to the breathable gas.Advantageously, supplying warm air with a temperature above body coretemperature results in less heat and water vapor loss from the subject'supper trachea with respect to prior systems. As mentioned herein, acomparatively cold and therefore dry air inflow, as seen in priorsystems, will induce a marked heat and vapor flow from the skin of theupper trachea of the subject. The skin of the upper trachea will thus becooled and dried out. This may lead to discomfort and an increased riskof infection and ciliary dysfunctionality. The droplets might not beable to prevent the drying out of the tracheal skin because only a smallfraction (e.g. 10-30%) of the droplets will be deposited at the tracheasurface. In some embodiments according to the present technology, areduced diameter of droplets is achieved, which gives the droplets amuch higher probability of reaching the airways without hitting thewalls of the tracheal cannula bend.

It is not advantageous to heat up the breathable gas after the moistureand/or droplets application because this process would take too long. Anadvantage in heating up the breathable gas before it reaches nebulizer16 is that the time needed to evaporate droplets 54 is much shorter andthus the required minimum distance between nebulizer 16 and subjectinterface 20 is much smaller (a short distance d, e.g., between about 1cm and 30 cm, although all other appropriate distances arecontemplated). That is one of the advantages of this design. Thetemperature gradient between the heated air and cold droplets 54 is highand therefore droplets 54 evaporate quickly. If you want to heat themixture of air plus droplets 54, then the temperature gradient betweenthe air surrounding droplets 54 and droplets 54 themselves is muchsmaller and therefore the evaporation takes longer.

A drawback of prior art “heated humidification” is that the devicecannot be placed close to the subject's trachea, because it is heavy andbulky, contains an open water reservoir, etc. Instead a “heatedhumidifier” is connected to the patient via more than one meter oftubing. Inside this tubing, water condensation will occur, since it isvery difficult to hold this long tubing at an elevated temperature.After some time, the tubing will contain appreciable amounts (up toseveral tens of ccm) of water. There is a risk of aspiration by thesubject. In contrast, some embodiments according to the presenttechnology advantageously only heat the room air and add water dropletsclose to the subject's trachea, so that the long tubing to the subjectremains dry.

In some embodiments, choosing a fixed, reasonable distance between thenebulizer and a subject and controlling operation/operating parameters(e.g., temperature, flow velocity, droplet size, heating power, etc.) isaccomplished in a way that an equilibrium between air and droplets 54 isestablished within this distance. “Equilibrium” as used herein mean thatno water is further evaporated (or condensed) from the droplets. A fastheating device (low-mass wire on high temperature) is implemented sothat the heating power could be adjusted proportionally to the air flowvelocity of the breathing pattern during inspiration.

In some embodiments, the tracheal cannula (conduit 28) has a bend, asmentioned herein. The tracheal cannula is communicatively coupled withpressure generator 14 (e.g., a ventilator). The tracheal cannula has aninner lumen diameter and the bend of the tracheal cannula has acurvature radius. The tracheal cannula is configured to supply thebreathable gas to the airway of subject 12. The inner lumen diameter andthe curvature radius facilitate the delivery of droplets to the tracheaof subject 12 such that the breathable gas received by subject 12exhibits a target temperature and humidity level. In some embodiments,the target temperature of about room temperature and a relative humidityare maintained at an interface (such as interface appliance 30) to thesubject, the relative humidity being about 100%.

In some embodiments, the inner lumen diameter falls within a range ofabout 4 mm to about 11 mm. These are merely exemplary ranges, and allother suitable ranges are contemplated. In some embodiments, thecurvature radius falls within a range of about 17 mm to about 25 mm.These are merely exemplary ranges, and all other suitable ranges arecontemplated. In some embodiments, the moisture may be in the form of amist of water droplets. The temperature of the breathable gas at thesubject interface ranges from about room temperature to a maximumpermitted temperature of 42° C. in some embodiments. Regarding humiditylevels, the total water content (water vapor and water droplets) of thegas entering the subject interface should fall within the range of about20 mg/L to about 44 mg/L, in some embodiments. In some embodiments, themist may also be from a saline solution.

In some embodiments, mesh 52 is a vibrating mesh nebulizer. Vibratingmesh nebulizers are known in the art. One exemplary vibrating meshnebulizer that may be used in some embodiments of the present technologyis manufactured by Aerogen, Inc. An example of a patent applicationrelated to a vibrating mesh nebulizer that is assigned to Aerogen, Inc.is US2007/0209659, which is incorporated herein by reference. Mesh 52 islocated in nebulizer 16 to generate a mist of water droplets 54 of adefined diameter in the range of about 2 μm to about 8 μm. A fasttemperature sensor is located at an entrance of the tracheal cannula tofacilitate controlling operating conditions including temperature,humidity, and other conditions mentioned in this disclosure. Fasttemperature sensors are known in the art and exhibit fastresponse/reaction times to changes in temperature. The fast temperaturesensor is configured to trigger a switch-off of heater 38 when athreshold temperature is reached at the entrance of the tracheal cannulaindicating that nebulizer 16 is failing to produce droplets. Thethreshold temperature would be set within the range of about 40° C. toabout 42° C. (current standards are limiting the temperature of an airstream to human airways to be less or equal 42° C.).

Processor 22 is configured to determine one or more parameters relatedto the pressurized flow of breathable gas. Processor 22 is configured todetermine the one or more parameters based on the output signals fromsensor 18 and/or other information. The one or more parameters relatedto the pressurized flow of breathable gas may comprise, for example, oneor more of a flow rate, a volume, a pressure, humidity of the gas,temperature of the gas, acceleration, velocity, ambient temperature, arelative ambient humidity, leak, the humidification method,humidification method set points (e.g., a target humidity level, heaterplate temperature, etc.), a subject interface (e.g., conduit)temperature, water usage (e.g., per hour and/or per session), altitude,home heating/cooling mode/settings, and/or other parameters. In someembodiments, processor 22 is configured to obtain operational statusindicators generated by pressure generator 14 and/or nebulizer 16, forexample, that indicate an operational status of the individualcomponent. The operational status indicators may indicate, for example,whether individual devices within a given component are operating asexpected. For example, heater 38 of nebulizer 16 provides heat whenrequired. The information determined by processor 22 may be used tocontrol system 10 according to a predetermined therapy regime, adjustthe therapy provided to subject 12, determine whether to prompt subject12 and/or other users to manually adjust one or more components ofprocessor 22, and/or for other uses.

Processor 22 is configured to control pressure generator 14, nebulizer16, and/or other components to deliver the pressurized flow ofbreathable gas to subject 12. Processor 22 is configured to controlpressure generator 14, nebulizer 16, subject interface 24, and/or othercomponents according to a predetermined therapy regime. Processor 22 isconfigured to control pressure generator 14, nebulizer 16, subjectinterface 24, and/or other components based on the output signals fromsensor 18, information determined by parameter component 40, and/orother information. By way of a non-limiting example, processor 22 maycontrol pressure generator 14 such that the pressure support provided tosubject 12 via the flow of gas comprises non-invasive or invasiveventilation, positive airway pressure support, continuous positiveairway pressure support, bi-level support, BiPAP®, and/or other types ofpressure support therapy.

In some embodiments, processor 22 is configured such that thepredetermined therapy regime is based on typical ambient weatherconditions during a given season of the year, previous feedbackinformation from subject 12 received during the given season,information from a thermostat controlling the temperature of theenvironment where pressure support therapy occurs, and/or otherinformation. Processor 22 may be configured to wirelessly (and/or viawires) communicate with external resources via a network (e.g., theInternet) to obtain such information. For example, processor 22 maydetermine the season of the year based on information retrieved from anexternal server that stores information related to the ambient weather.Processor 22 may obtain previous feedback information from subject 12that is stored in electronic storage 50, for example, and/or in otherlocations. The information may be stored in electronic storage 50 withidentifiers that convey when the information (e.g., the date) wasreceived and/or stored, for example. Processor 22 may retrieveinformation from the thermostat controlling the temperature of theenvironment via a local area network and/or other networks, for example.

Processor 22 is configured to receive feedback information enteredand/or selected through user interface 20. Processor 22 is configured toreceive entry and/or selection of feedback information from subject 12indicating an initial comfort level with the pressurized flow ofbreathable gas. After an automatic adjustment to the pressurized flow ofbreathable gas (described herein), processor 22 is configured to receiveentry and/or selection of additional feedback information from subject12 indicating an adjusted comfort level. In some embodiments, processor22 is configured to control user interface 20 to present one or moreviews of a graphical user interface to subject 12 that facilitate entryand/or selection of the feedback information. In some embodiments, thefeedback information includes information related to an inhaled airtemperature, an inhaled air moisture, whether or not subject 12 hasexperienced tube rainout, whether or not subject 12 has experienced maskrainout, and/or other information.

In some embodiments, processor 22 may be configured such that the one ormore views of the graphical user interface presented to subject 12 viauser interface 20 facilitate rating at least some portions of thefeedback information according to a predetermined ratings scale. Forexample, processor 22 may facilitate rating the inhaled air temperature(e.g., 0 being too cold, 10 being too hot), rating the inhaled airmoisture (e.g., 0 is too dry, 10 is too wet), and/or rating otherfactors.

Processor 22 is configured to make an automatic adjustment to thepressurized flow of breathable gas to enhance the comfort level ofsubject 12. The automatic adjustment may be made based on the receivedfeedback, the output signals from sensor 18, the information determinedby various components, and/or other information. The automaticadjustment may include adjustment of pressure generator 14, nebulizer16, subject interface 24, and/or other components of system 10.

In some embodiments, as described above, user interface 20 and/orprocessor 22 is configured to receive additional feedback informationentered and/or selected through user interface 20 subsequent to anautomatic adjustment. In some embodiments, additional automaticadjustments are made to the pressurized flow of breathable gas toenhance the comfort level of subject 12. The additional automaticadjustment may be made based on the additional feedback information, theoutput signals from sensor 18, the information determined by processor22, and/or other information.

The additional automatic adjustment may include adjustment of pressuregenerator 14, nebulizer 16, subject interface 24, and/or othercomponents of system 10. In some embodiments, processor 22 is configuredsuch that the adjustment, feedback, adjustment process is repeated(e.g., iterated) one or more times. Processor 22 may be configured torepeat the adjustment and feedback cycle when the feedback informationindicates that the comfort level of subject 12 is improving, forexample. In some embodiments, processor 22 is configured to ceaseautomatic adjustments responsive to the feedback information indicatingthat subject 12 is comfortable, the feedback information indicating thatthe comfort level of subject 12 is not improving (e.g., the temperatureof the inhaled air is still too cold for subject 12, rainout stilloccurs even after all of the automatic adjustments, etc.), and/or forother reasons.

Processor 22 is configured to determine whether to prompt subject 12and/or other users to make a manual adjustment to system 10 and/orexternal factors associated with system 10. Processor 22 may beconfigured to control user interface 20 to prompt subject 12 and/orother users. The manual adjustment may include, for example, manualadjustments to one or more components of system 10, manual adjustmentsto the ambient environment, manually adjusting the therapy location,and/or other manual adjustments. A manual adjustment may include anadjustment to pressure generator 14, nebulizer 16, subject interface 24,and/or other components of system 10.

In some embodiments, the prompted manual adjustment includes changingthe temperature of the ambient environment, changing a type of therapyof the predetermined therapy regime, changing physical components of thepressure support system (e.g., adding and/or removing a heater forconduit 28), changing the tank capacity of nebulizer 16, changing a mask(e.g., interface appliance 30) that has excessive leak), and/or othermanual adjustments. In some embodiments, the manual adjustments includemanually changing therapy set points (e.g., target humidity level,target temperature, etc.) via user interface 20, for example.

Processor 22 is configured to determine whether to prompt subject 12and/or other users based on the additional feedback informationsubsequent to the automatic adjustment, the output signals from sensor18, the information determined by various components, the automaticadjustments to the pressurized flow of breathable gas, and/or otherinformation.

In some embodiments, processor 22 is configured such that subject 12and/or other users are prompted to make a manual adjustment only ifnecessary. Subject 12 and/or other users may be prompted to make amanual adjustment if the automatic adjustment to the pressurized flow ofbreathable, for example, gas does not enhance the comfort level ofsubject 12, does not enhance the comfort level by a predeterminedamount, and/or for other reasons. For example, processor 22 may beconfigured to prompt subject 12 to try a different pressure generator,nebulizer, and/or subject interface (e.g., prompt a switch from asubject interface that does not include a heater to one that doesinclude a heater), and/or run a system diagnostic if the presentcomponents of system 10 are unable to be adjusted enough to satisfy theneeds of subject 12.

The description of an automatic adjustment by processor 22 and then, ifnecessary, a prompted manual adjustment is not intended to be limiting.In some embodiments, processor 22 is configured to prompt subject 12and/or other users to make a manual adjustment before any automaticadjustment by processor 22. In these embodiments, processor 22 may notmake an automatic adjustment at all and/or make an automatic adjustmentonly after processor 22 prompts manual adjustment.

In some embodiments, processor 22 is configured to provide feedback tosubject 12 via user interface 20 and/or other components of system 10.For example, processor 22 may be configured to notify subject 12 if acomponent(s) obtains operational status indicators that indicate, forexample, that individual devices within a given component are notoperating as expected (e.g., heater 38 of nebulizer 16 does not provideheat when required, sensor 18 is out of range, expected leak is out ofrange, environmental conditions exceed system capabilities, pressuregenerator 14 malfunctions, and/or feedback components are unavailable.)

By way of a non-liming example, FIG. 2 illustrates of a view 200 of userinterface 20 presented to subject 12 (FIG. 1) and/or other users. InFIG. 2, user interface 20 is integral with pressure generator 14. View200 includes parameter fields 202, 204, 206, and 208, a feedbackinformation field 210, and a manual adjustment prompt field 212. One ormore components of processor 22 may control user interface 20 (asdescribed above) to provide information to and/or receive informationfrom subject 12 and/or other users. For example, one or more parametersdetermined by parameter component 40 may be displayed to subject 12 viaparameter fields 202-208. Parameters such as ambient temperature,ambient relative humidity, the type of pressure support therapy and/orhumidification, pressure support therapy and/or humidification setpoints, leak, an operational status indicator (e.g., indicating whethercomponents of system 10 are operating normally), and/or otherparameters.

Feedback information field 210 is configured to receive entry and/orselection of feedback information from subject 12 and/or other users.Field 210 may be touch sensitive (e.g., a touchscreen) so that subject12 and/or the other users may enter information by touching field 210.Field 210 may display information entered via a keyboard, keypad, and/orother entry device.

Manual adjustment prompt field 212 may be configured to display promptsto the user to facilitate adjustment of system 10, make recommendationsto subject 12, and/or provide other information. For example, field 212may display messages such as, “Increase the room temperature,” and/or,“Change to a subject interface that includes a heated tube,” and/orother informational messages. Recommendations may be related to, forexample, the pressure support therapy and/or humidification method,pressure support therapy and/or humidification method set points, and/orother information.

By way of a second non-limiting example, FIG. 3 illustrates a view 302of user interface 20 presented to subject 12 (FIG. 1) and/or other usersvia a display of a smartphone 300 and/or other mobile computing deviceassociated with subject 12. View 302 includes feedback information field304. In the example shown in FIG. 3, processor 22 (FIG. 1) hascontrolled field 304 to display survey questions 308. The surveyquestions are configured to facilitate entry and/or selection ofinformation related to the comfort level of subject 12 during therapy.In the example shown in FIG. 3, subject 12 may provide information bydragging and dropping an indicator 310, 312 on a scale of 1 to 10,and/or activating YES/NO indicators 314. These options are not intendedto be limiting. Processor 22 may control field 304 to facilitate entryand/or selection of comfort level information in any way that allowssystem 10 to operate as described herein.

FIG. 4 illustrates a system 400 configured to facilitate humidificationof a pressurized flow of breathable gas delivered to a subject. System400 is similar to system 10 of FIG. 1. Pressure generator (pressurizingdevice) 14 is communicatively coupled with (fast air) heater 38. In someembodiments, as illustrated, conduit 28 passes through heater 38.Nebulizer 16 includes vibrating mesh nebulizer 52 that iscommunicatively coupled with a supply to a water reservoir. Waterdroplets 54 are emitted from vibrating mesh nebulizer 52.

FIG. 5 illustrates a simulation model of a personal nebulizer 500 ofsystem 10. In some embodiments, personal nebulizer 500 may include oneor more of the tracheal cannula, conduit 28, subject interface 24,interface appliance 30, and/or other elements. The vertical portion ofthe tube represents a trachea. The numbers shown indicate millimeters.The model is isothermal at 20° C.; the reference pressure is 1 atm. Theinner tube diameter is 16 mm; the curvature radius of the bend is 50 mm.Air is entering from the left at a peak flow rate of 70 L/min. Thevertical tube represents the trachea. The overpressure at its lower end(the outlet) is set to zero. As a first study a stationary laminar flowsolution is calculated. The entrance overpressure is 0.09 mbar (9 Pa);the average flow velocity at the outlet/inlet is 5.90 m/s. The Reynoldsnumber for this peak flow is 6100; therefore the assumption of laminarflow is not justified, since purely laminar flow can be generallyassumed (in the case of tubes) for Reynolds numbers <2300 and turbulentflow has to be assumed for Rey >4000. Nevertheless laminar flowcalculations were performed for simplicity reasons. The pressure movingfrom the left end to the lower end ranged from about 0.76 mbar to about0.00 mbar.

As a second study a simulation was performed that is referred to as“Particle Tracing for Fluid Flow.” 100 uncharged spherical particles(water droplets) were released at the air inlet at t=0 with ahomogeneous distribution over the inlet surface. Their initial velocitywas the flow velocity; their density was 1 kg/L, and their diameter was5 μm. These droplets are then followed in time under influence of aStokes drag force. If a droplet would hit a wall, it would stick to thewall with 100% probability. Droplets reaching the outlet were recordedthere with their velocity. In the simulation, 21 droplets hit a wall and79 droplets have reached the outlet. The simulated transmissionprobability was thus 79%.

FIG. 6 illustrates a simulation model of a personal nebulizer 600 ofsystem 10. In some embodiments, personal nebulizer 600 may include oneor more of the tracheal cannula, conduit 28, subject interface 24,interface appliance 30, and/or other elements. The numbers shownindicate millimeters. The simulation is related to the geometry of the22 mm inner diameter supply tube, a conical connector piece (15 mm long,final diameter 16 mm) and a “Tracheoflex S” trach with an 8 mm innerdiameter. The trach length dimensions are: intratracheal tubular partA=32.5 mm, extratracheal tubular part B=12.7 mm, bent length C=31.4 mm,trach angle q=90° (for geometrical simplicity; true angle is 95°). After0.5 s, 12 droplets have hit a wall, 1 droplet is still in the tubevolume, and 8 droplets are lost. Air is entering from the left at a peakflow rate of 70 L/min. The vertical tube represents the trachea. Theoverpressure at the lower end (the outlet) is set to zero. As a firststudy a stationary laminar flow solution was calculated. The entranceoverpressure was 8.39 mbar; the average flow velocity at the inlet was3.10 m/s, the average flow velocity at the outlet was 24.3 m/s. The peakflow Reynolds number is 12200. Therefore the assumption of laminar flowis not justified anymore. Nevertheless (for simplicity reasons) alaminar flow calculation was performed. The pressure moving from theleft end to the lower end ranged from about 8.2 mbar to about 0.03 mbar.The air velocity moving from the left end to the lower end ranged fromless than 5 m/s to over 30 m/s.

In a second study a simulation referred to as “Particle Tracing forFluid Flow” was performed. 100 uncharged spherical particles waterdroplets) were released at the air inlet at t=0 with a homogeneousdistribution over the inlet surface. Their initial velocity is the flowvelocity, their density was 1 kg/L, and their diameter was 5 μm. Thesedroplets were then followed in time under influence of a Stokes dragforce. If a droplet will hit a wall, it would stick to the wall with100% probability. Droplets reaching the outlet were recorded there, withtheir velocity. After 0.2 s, 98 droplets hit a wall, whereas only 2droplets reached the outlet. The simulated transmission probability wasthus 2%.

System 10 can be simulated using a droplet model based on Newtonianinertia and a Stokes drag force. Other mechanisms such as droplet growthby water vapor condensation or droplet coagulation apparently do notplay a role. This seems reasonable, because these are comparatively“slow” processes, whereas the time scale for the observed disappearanceof 5 μm droplets is in the order of 1 ms (0.01 m/(10 m/s)) (i.e. quite“short”). After 0.5 s, 6 droplets have hit the conical connector wall,26 droplets have hit the “step” between the connector and trach, 62droplets have hit the “trach” walls, 1 droplet is still in the volume ofthe supply tube, and 3 droplets are “lost.”

The Stokes drag force for spherical particles in low Reynolds numberflows is

$F_{s} = {6\; {\pi \cdot \mu \cdot \frac{d_{p}}{2} \cdot \left( {v_{F} - v_{p}} \right)}}$

where μ=air dynamic viscosity (1.86E-5s*Pa at 25° C.), d_(p)=particlediameter (5 μm), _(F)=fluid velocity vector [m/s], v_(p)=particlevelocity vector [m/s]. In Comsol this is written as

$F_{s} = {\frac{m_{p}}{\tau_{p}} \cdot \left( {v_{F} - v_{p}} \right)}$

with the “particle velocity response time”

$\tau_{p} = {\frac{\rho_{p} \cdot d_{p}^{\; 2}}{18\mu} = {0.075\mspace{14mu} {ms}\mspace{14mu} {\left( {\rho_{p} = {{particle}\mspace{14mu} {density}\mspace{11mu} \left( {1\mspace{11mu} {kg}\text{/}L} \right)}} \right).}}}$

For a maximum gas/particle velocity of 30 m/s this is corresponding to adistance travelled of 2.2 mm. It will take a certain multiple (≈3) of“response times” (or, respectively, a distance travelled Δx_(equal)≈7mm) before gas and particle velocities are really “identical”.

Thus, a first consequence of this “short” particle velocity responsetime is that the droplets will be accelerated to the suddenly increasedgas velocity at the trach entrance (where the velocity vectors of gasand particle are parallel) within few tenths of a millisecond, i.e.within less than a cm distance travelled.

What is happening in the bend of the trach should be considered. It canbe noticed that the distance Δx_(equal)≈7 mm is already 34% of thecurvature radius of the bend (20mm). Therefore, one may expect that alarge fraction of the droplets will have problems to traverse the bendwithout hitting the right wall.

Looking at the distribution of gas velocity vectors in the trach, thegas flow is “squeezed” towards the right wall when traversing the bend.This means that the gas velocity vectors will remain nearly parallel tothe horizontal axis for a long time (i.e. until x≈35 mm) beforedeveloping a component in the −y direction. This is especially true forparticles above the center line y=0 (the middle of the left opening).For those particles the −y component of the Stokes drag force is toosmall to “bend” their particle velocity vector before the particle hitsthe tube wall.

This is confirmed if one looks at the traces of the 2 particles that areeventually transmitted. It is easily seen that these particles are theones entering the trach with the lowest possible y-coordinate so thatthey will experience a considerable Stokes drag force component in −ydirection during a long distance so that they are just able to avoid acollision with the “right” wall.

For a geometry referred to as “Uniform tube radius & large curvatureradius of bend”), the situation is much more favorable for the droplets.The maximum gas/particle velocity is now ≈7 m/s, which implies that the“particle velocity response time”

$\tau_{p} = {\frac{\rho_{p} \cdot d_{p}^{\; 2}}{18\mu} = {0.075\mspace{14mu} {ms}}}$

is now corresponding to a distance travelled of 0.52 mm.

As stated above it will take a certain multiple (≈3) of “response times”(or, respectively, a distance travelled Δx_(equal)≈1.6 mm) before gasand particle velocities are really “identical.” This distance travelledis only 3% of the curvature radius of the bend (50 mm); therefore themajority of the droplets will now be able to bend down before hittingthe right wall.

For a “trach”-like geometry with “suddenly decreasing tube radius &small curvature radius of bend,” a large fraction of droplets (˜98%)will hit the tube wall at the trach entrance and at the trach bend.

The physical mechanism needed to explain the droplet trajectories isjust Newtonian inertia and a Stokes drag force. “Slower” mechanisms likedroplet growth by water vapor condensation or droplet coagulation do notplay a role.

The fraction of droplets hitting the bend of the trach is a monotonouslyincreasing function of the ratio of Δx_(equal) (the distance travelledbefore gas and particle velocities are equal) to the bend curvatureradius. For Δx_(equal) one may use the estimateΔx_(equal)≈3*v_(max)*τ_(p) where v_(max)=maximum gas velocity and

$\tau_{p} = {\frac{\rho_{p} \cdot d_{p}^{\; 2}}{18\mu}.}$

The preceding considerations can be cast into a practical guideline toavoid that a large fraction of droplets is hitting the wall: Define an“impaction criterion” (IC) which should be less than one, if most of thedroplets should be transmitted through a certain bend within the tube:

${{a.\mspace{14mu} {IC}} = {\frac{d_{p}^{\; 2} \cdot \varphi}{{{D_{t}^{\; 2} \cdot R_{c} \cdot 5.}E} - {6\mspace{14mu} L\text{/}\left( {\min \cdot {cm}} \right)}} < 1}},$

where d_(p)=droplet diameter, Φ=air flow, D_(t)=tube diameter,R_(c)=tube bend curvature radius.

In the example of FIG. 5 (as discussed above) we have d_(p)=5 μm, Φ=70L/min, D_(t)=16 mm, R_(c)=50 mm and thus IC=0.273 which is fulfillingthe limiting condition IC<1. This is consistent with our FEM simulationwhich resulted in 79% transmission probability of those droplets.

FIG. 7 illustrates a simulation model of a personal nebulizer 700 ofsystem 10. In some embodiments, personal nebulizer 700 may include oneor more of the tracheal cannula, conduit 28, subject interface 24,interface appliance 30, and/or other elements. The numbers shownindicate millimeters. This geometry can be referred to as a “smoothlydecreasing tube radius and small curvature radius of bend.”

The pressure distribution (entrance over-pressure is 7.38 mbar) rangesfrom about 7.22 mbar at the left entrance to about 0.04 mbar at thebottom outlet. The average flow velocity at the inlet is 3.10 m/s. Theaverage flow velocity at the outlet is 24.3 m/ s.

The particle positions after 0.2 s were examined. Out of 100 droplets,26 droplets reached the outlet. Thus, the transmission probability is26% (compared to 2% in a prior simulation mentioned herein). Thedetailed distribution of the other droplets after 0.5 s is that 21droplets hit the conical connector walls; 43 droplets hit the “trach”walls; 0 droplets are still within the gas volume, and 10 droplets are“lost.”

Various simulations have been performed with respect to some embodimentsof a personal nebulizer according to the present technology. Some ofthese simulations related to the evaporation behavior of droplets.

A summary of some simulations that have been performed for system 10 andthe operation thereof, including the personal nebulizer of system 10,include:

(1) A simulation was performed using a macroscopic model of water vapordiffusion and heat conduction assuming thermodynamic equilibrium ofwater vapor and liquid water at the droplet's surface. “Macroscopic”means that no individual droplets have been considered. Instead, themist of droplets is seen as one homogeneous medium. Water vapordiffusion and heat conduction are strongly coupled by “instantaneous”evaporation/condensation as long as there are droplets. The waterdroplets just increase the effective “diffusivity of heat” by a certainamount (˜12%).

(2) A “particle tracing” FEM model of particle movement in a “dry” airflow of constant temperature. Here the aim was to find the fraction ofwater droplets hitting the tube wall in a bend. Simple physics (inertiaand drag force) were included in the simulation, but a full 3D geometrywas simulated. This special model is separated from the others.

(3) An FEM study of temperatures, flow velocities, water vapor in arotationally symmetric “trachea” (cylinder) with surrounding tissue. Asimple geometry was used, but a complete breathing pattern (inhalationand exhalation) was simulated. There were no water droplets added to thegas stream. During inhalation the temperature and humidity of theinhaled air stay almost constant. The (upper) trachea walls deliver onlya small fraction of the total amount of heat and water vapor that istransferred to the inhaled and exhaled air volume. The largest part isof these heat and moisture losses is brought up by the lower airways.

Droplets injected into room air are generally not in equilibrium withthe gas. Usually there will be water vapor diffusion from the dropletsand heat transfer from the surrounding gas, and one will numericallyanalyze these coupled phenomena in a spherical (1D) Mathcad modeldescribing the transport phenomena in the volume occupied by onedroplet. The addressed questions include the following.

It was found that there are actually two time scales: a) rapidevaporation and cooling of a droplet until equilibrium at its surface isestablished; and b) slower water vapor diffusion from the dropletsurface and heat transfer from the gas to the droplet surface.

Regarding final temperature and water vapor concentration, a certainamount of water vapor will evaporate from each droplet. This will leadto a temperature decrease of the droplet (and its surrounding gas),because the water evaporation enthalpy has to be brought up. In thefinal situation, the water vapor concentration n_(f) is at equilibriumwith the final temperature T_(f) and the total heat gained by cooling isequal to the total evaporation enthalpy of the evaporated watermolecules. This gives a system of two equations with two unknowns (n_(f)and T_(f)):

$\begin{matrix}{{n_{f} \cdot k_{B} \cdot T_{f}} = {p_{v}\left( T_{f} \right)}} & {{\Delta \; {{H\left( T_{a} \right)} \cdot \frac{n_{f} - n_{r}}{N_{A}}}} = {\left( {T_{r} - T_{f}} \right) \cdot {C_{pt}\left( T_{a} \right)}}}\end{matrix}$

Where p_(v)(T)=water vapor pressure [Pa], ΔH(T_(a))=water evaporationenthalpy [44.1 kJ/mol] evaluated at an average temperature T_(a)=23° C.,T_(r)=supplied air temperature, n_(r)=supplied air water vapor density[1/m³], C_(pt)(Ta)=total heat capacity of droplets and air [1311J/K/m³].

The following is an example: T_(r)=20° C., n_(r)=3.68*10²³ [1/m³] (=11mg/L) →T_(f)=15.59° C. and n_(f)=4.47*10²³ [1/m³] (=13.4 mg/L).

The air temperature will thus decrease by 4.4 K and the water vaporconcentration will increase by 21%.

Regarding the volume occupied per droplet, the initial mass of one waterdroplet is

$m_{d} = {{1{\frac{kg}{L} \cdot \frac{4}{3}}\mspace{11mu} \pi \mspace{11mu} \left( \frac{D_{d}}{2} \right)^{3}} = {{6.545 \cdot 10^{- 8}}\mspace{11mu} {{mg}\;.}}}$

The initial number of water molecules in one droplet is thus

$N_{d} = {\frac{m_{d}}{18{AMU}} = {2.19 \cdot {10^{12}.}}}$

The initial droplet concentration is c_(l)=33 mg/L. The initial densityof water droplets is thus n_(l)=c_(l)/m_(d)=5.04*10⁸ droplets/L. The gasvolume “occupied” by one droplet is thus

${V_{{oc}\mspace{11mu} c}\text{:}} = {\frac{1}{n_{1}} = {1.983 \times 10^{- 9}\mspace{11mu} L}}$

The number of molecules evaporated from one droplet is thus

N _(evap):=(n _(f) −n _(r))·V _(occ)=1.563×10¹¹

This is about 7.1% of the initial number of molecules in one dropletN_(d).

Regarding the time scale of evaporation and condensation, this timescale can be obtained by simple arguments from the kinetic theory ofgases:

The collision rate Z [1/s] of water molecules with a certain waterdroplet is:

Z=n·Q·v _(re)

where n=density of water molecules [1/m³], Q=collisioncross-section=cross-section of water droplet [m²], v_(rel)=relativevelocity of molecule and droplet=thermal velocity of water molecules[m/s].

At 20° C. room temperature there is a water vapor equilibrium density of

${n_{e}\text{:}} = {\frac{p_{v}\left( T_{r} \right)}{k_{B} \cdot T_{r}} = {5.796 \times {10^{23} \cdot \frac{1}{m^{3}}}}}$

The cross-section of a water droplet with diameter D_(d)=5 μm is

$A_{d}:={{\pi \cdot \left( \frac{D_{d}}{2} \right)^{2}} = {1.963 \times 10^{- 11}m^{2}}}$

The thermal velocity of the water vapor molecules is

${v_{rel}\text{:}} = {\sqrt{\frac{3 \cdot k_{B} \cdot T_{r}}{\left( \frac{M_{H\; 2O}}{N_{A}} \right)}} = {637.353\mspace{11mu} \frac{m}{s}}}$

Taking into account that only half of the molecules will fly toward thedroplet surface we set n=n_(e)/2 and find

$Z:={{\frac{n_{e}}{2} \cdot A_{d} \cdot v_{rel}} = {3.626 \times 10^{15}\frac{1}{s}}}$

The evaporation rate ER of molecules from the water droplet isproportional to its surface S=4A_(d) with a temperature-dependentproportionality constant k_(E)(T): ER=4*A_(d)*k(T). In thermodynamicequilibrium we have Z=ER, leading to this expression for k_(E)(T):

${{{k_{E}(T)}\text{:}} = \frac{p_{v}(T)}{8}}{\cdot \sqrt{\frac{3 \cdot N_{A}}{M_{H\; 2O} \cdot \left( {k_{B} \cdot T} \right)}}}$

Referring back to the example: At the initial temperature T_(r)=20° C.the evaporation rate is

${{ER}\text{:}} = {{4 \cdot A_{d} \cdot {k_{E}\left( T_{r} \right)}} = {3.626 \times 10^{15}\frac{1}{s}}}$

and the condensation rate (collision rate) is

${Z\text{:}{= \frac{n_{r}}{2} \cdot A_{d} \cdot v_{rel}}} = {2.303 \times 10^{15}\frac{1}{s}}$

The time constant for droplet evaporation is thus

$\tau_{ev}:={\frac{N_{evap}}{{ER} - Z} = {0.118 \cdot {ms}}}$

This time constant is indeed very small compared to the time scale ofthe breathing cycle—and also small compared to the time scale fordiffusion/heat conduction. It is therefore meaningful to assumeevaporation/condensation as “fast” (not rate-limiting) processes.

Regarding a time scale of water vapor diffusion and heat conduction, asstated, one can construct a 1D model with spherical symmetry which iscovering the volume V_(occ) occupied by one water droplet. The dropletradius is R_(d)=D_(d)/2=2.5 μm.

The radius R_(occ) of the occupied volume is:

$R_{occ}:={\sqrt[3]{\frac{3}{4 \cdot \pi} \cdot V_{occ}} = {77.941 \cdot {\mu m}}}$

The water vapor diffusion equation can be examined. The water vaporcontinuity equation and Fick's diffusion law are reading:

$\begin{matrix}{{{\frac{\partial}{\partial t}n} + {\nabla{\cdot j_{n}}}} = 0} & {j_{n} = {{- D} \cdot {\nabla n}}}\end{matrix}$

With n=water vapor density [1/m³], j_(n)=water vapor flux density[1/m²/s], D=water vapor diffusion coefficient (2.62*10⁻⁵ m²/s at 30° C.,1 atm). In spherical coordinates we have:

${{\frac{\partial}{\partial t}n} - {D \cdot \left\lbrack {{\frac{1}{R} \cdot \frac{\partial^{2}}{\partial R^{2}}}\left( {R \cdot n} \right)} \right\rbrack}} = 0$

We assume a certain time dependence of n(t,R) to be able to separate thevariables t and R (and to transform this PDE into an ODE):

${n\left( {t,R} \right)} = {{\left( {n_{f} - {n_{s}(R)}} \right) \cdot \left( {1 - e^{\frac{- t}{\tau_{d}}}} \right)} + {n_{s}(R)}}$${{\frac{d^{2}}{d\; R^{2}}{n_{s}(R)}} + {{\frac{2}{R} \cdot \frac{d}{dR}}{n_{s}(R)}} - \frac{\left( {n_{f} - {n_{s}(R)}} \right)}{\tau_{d} \cdot D}} = 0$

This means that n(t,R) will start with a certain distribution n_(s)(R)and evolve into a homogeneous final distribution of with a “diffusion”time constant τ_(d). We thus obtain this ODE for the start distributionn_(s)(R):

The two boundary conditions for integration are:

${j_{n}\left( {t,R_{occ}} \right)} = {{0\mspace{11mu} \left( {{no}\mspace{14mu} {loss}\mspace{14mu} {of}\mspace{14mu} {molecules}\mspace{14mu} {from}\mspace{14mu} V_{occ}} \right)\mspace{14mu} \mspace{14mu} \frac{d}{d\; R}{n_{s}\left( R_{occ} \right)}} = 0}$

n_(s)(R_(occ))=n_(r) (the start water vapor density at the edge ofV_(occ) is the initial air concentration n_(r)).

The diffusion time constant τ_(d) is yet unknown and will be determinedlater.

Examining the heat conduction equation, the energy balance equation isreading:

$\begin{matrix}{{{\frac{\partial}{\partial t}u} + {\nabla{\cdot j_{E}}}} = 0} & {\; {u = {c_{a} \cdot C_{pa} \cdot T}}} & {j_{E} = {{- \lambda} \cdot}}\end{matrix}{\nabla T}$

With u=energy density [J/m³], j_(E)=energy flux density [W/m²],c_(a)=air concentration [1.166 kg/m³], C_(pa)=air heat capacity [1006J/kg/K], λ=air thermal conductivity [0.026 W/m/K]. In sphericalcoordinates:

${{\frac{\partial}{\partial t}T} - {\alpha_{a} \cdot \left\lbrack {{\frac{1}{R} \cdot \frac{\partial^{2}}{\partial R^{2}}}\left( {R \cdot T} \right)} \right\rbrack}} = {0\mspace{14mu} {with}}$$\alpha_{a}:={\frac{\lambda \left( T_{a} \right)}{c_{a} \cdot {C_{pa}\left( T_{a} \right)}} = {2.218 \times 10^{- 5}\frac{m^{2}}{s}}}$

We assume again a certain time dependence of T(t,R):

${T\left( {t,R} \right)} = {{\left( {T_{f} - {T_{s}(R)}} \right) \cdot \left( {1 - e^{\frac{- t}{\tau_{E}}}} \right)} + {T_{s}(R)}}$

The start temperature distribution T_(s)(R) should fulfill this ODE:

${{\frac{d^{2}}{{dR}^{2}}{T_{s}(R)}} + {{\frac{2}{R} \cdot \frac{d}{dR}}{T_{s}(R)}} - \frac{\left( {T_{f} - {T_{s}(R)}} \right)}{\tau_{E} \cdot \alpha_{s}}} = 0$

The first boundary condition is: T_(s)(R_(d))=TsL (the start temperatureat the droplet surface is TsL).

The second boundary condition is derived from the integral energybalance of the droplet:

${{- m_{d}} \cdot C_{pl} \cdot \left( {\frac{\partial}{\partial t}{T\left( {t,R_{d}} \right)}} \right)} = {4 \cdot \pi \cdot {R_{d}}^{2} \cdot \left( {{\frac{\Delta \; H}{N_{A}} \cdot {j_{n}\left( {t,R_{d}} \right)}} + {j_{E}\left( {t,R_{d}} \right)}} \right)}$

The left hand side term is the energy gain by cooling of the droplet [inW]. The first term on the right hand side is the energy loss byevaporation of water molecules and the second term on the RHS is theenergy gain by heat conduction from the gas. Rearranging for j_(E) wehave:

${j_{E}\left( {t,R_{d}} \right)} = {\frac{{{- m_{d}} \cdot {C_{pl}\left( T_{a} \right)} \cdot \frac{\partial}{\partial t}}{T\left( {t,R_{d}} \right)}}{4 \cdot \pi \cdot {R_{d}}^{2}} - {\frac{\Delta \; H}{N_{A}} \cdot {j_{n}\left( {t,R_{d}} \right)}}}$

This implies that the temperature dependence of j_(n)(t,R_(d)) ∝exp(−t/τ_(d)) should be the same as the temperature dependence of dT/dtand j_(E)(t,R_(d)) (both ∝ exp(−t/τ_(E))). Therefore, we findτ_(E)=T_(d).

Evaluating the last equation at t=0 we find as second boundarycondition:

${\frac{d}{dR}{T_{s}\left( R_{d} \right)}} = {{\frac{\Delta \; H}{N_{A} \cdot {\lambda \left( T_{a} \right)}} \cdot {j_{ns}\left( R_{d} \right)}} + \frac{m_{d} \cdot {C_{pl}\left( T_{a} \right)} \cdot \left( {T_{f} - {TsL}} \right)}{{4 \cdot \pi \cdot {R_{d}}^{2} \cdot {\lambda \left( T_{a} \right)}}{\cdot \tau_{d}}}}$

However, there are still two unknown parameters: τ_(d) andTsL=T_(s)(R_(d)). These two parameters have to be iteratively adjusteduntil the last 2 boundary conditions are fulfilled:

${n_{s}\left( R_{d} \right)} = {\frac{p_{v}({TsL})}{k_{B} \cdot {TsL}}\left( {{thermodynamic}\mspace{14mu} {equilibrium}\mspace{14mu} {at}\mspace{14mu} {the}\mspace{14mu} {droplet}\mspace{14mu} {surface}} \right)}$${J_{E}\left( {t,R_{occ}} \right)} = {{0\mspace{11mu} \left( {= {{no}\mspace{14mu} {loss}\mspace{14mu} {of}\mspace{14mu} {energy}\mspace{14mu} {from}\mspace{14mu} V_{occ}}} \right)\mspace{14mu} \mspace{14mu} \frac{d}{dR}{T_{s}\left( R_{occ} \right)}} = 0}$

In the example from above one obtains a consistent solution forτ_(d)=2.525 ms and TsL=T_(s)(R_(d))=15.31° C.

Note that TsL (the start temperature at the droplet radius) is slightlylower than the final, homogeneous temperature T_(f)=15.59° C.(Correspondingly, the start density at the droplet radiusn_(s)(Rd)=4.39*10²³ 1/m³ is slightly lower than the final, homogeneousdensity n_(f)=4.47*10²³ 1/m³).

When comparing T_(d)=2.525 ms to the evaporation time τ_(ev)=0.12 ms, itshows that the evaporation is “fast” compared to diffusion andconduction. Note that T_(s)(R_(occ))=20.52° C., i.e., 0.52° C. higherthan the start temperature T_(r)=20° C. of the droplet plus room airensemble. This is a consequence of energy conservation: If the dropletis cooling by 4.4° C. by “fast” evaporation, then the air has to warm upso that the total energy is staying constant.

The distance travelled during 2*τ_(d) is examined. It is interesting toestimate the distance the air inhaled by the subject will have travelleduntil, say, 90% of the equilibrium between droplets and gas has beenestablished. The total volume inhaled is V_(inh)=0.5 L. The duration ofinhalation is t_(inh)=1 s. A typical tube diameter is 20 mm,corresponding to a tube cross section of A_(T)=3.14 cm². The average gasvelocity in the tube during inhalation is thus

$v_{avinh}:={\frac{V_{inh}}{A_{T} \cdot t_{inh}} = {1.592\frac{m}{s}}}$

90% of the equilibrium between droplets and gas has been establishedafter 2*τ_(d)=5.05 ms. Finally, the average distance travelled by themist in the tube during this time is v_(avinh)*2*τ_(d)=0.80 cm.

This implies that the equilibrium between water droplets and surroundinggas will be already established before the mist comes into contact withthe subject's tissue. It should be noted that the peak gas velocity onthe axis during inhalation is v_(pinh)=(70 L/min)/(30L/min)*2*v_(avinh)=7.43 m/s, i.e., a factor of 4.7 higher thanV_(avinh). The peak distance travelled on the axis until equilibrium isestablished is thus 0.80 cm*4.7=3.7 cm.

The transport phenomena in the occupied volume V_(occ) for our“standard” conditions (T_(r)=20° C. and c_(l)=33 mg/L) is discussedherein. Further examples (questions) also considered include:

Which temperature should the supplied air have to (nearly) completelyevaporate the injected droplets (c_(l)=33 mg/L)? What would the timeuntil equilibrium τ_(d) be in this case?

Which temperature should the supplied air have, if one is aiming at afinal equilibrium temperature of 25° C.? (This would be equivalent to a“conventional” humidifier supplying 100% RH at 25° C.). In this case wecould also reduce the injected droplet concentration (e.g. to c_(l)=16mg/L). What would the time until equilibrium τ_(d) be in this case?

Let us supply air and droplets at T_(r)=20° C. and c_(l)=16 mg/L and doa slow heating (without overshoot of temperature) after the injection ofdroplets so that the final equilibrium temperature is also 25° C. Whatwould the time until equilibrium Td and the heating power be in thiscase?

The results of simulations are summarized in the following table:

T_(r) = 20° C., c_(l) = T_(f) = 37° C., T_(f) = 25° C., Slow Parameter33 mg/L c_(l) = 33 mg/L c_(l) = 16 mg/L heating Start temperature T_(r)20° C. 95° C. 48° C. 20° C. Start vapor conc. c_(r) 11 mg/L 11 mg/L 11mg/L 11 mg/L Start rel. humidity 63.5%   2% 14.4% 63.5% Start dropletconc. c_(l) 33 mg/L 33 mg/L 16 mg/L 16 mg/L Start droplet radius 2.5 μm2.5 μm 2.5 μm 2.5 μm R_(d) Final temperature T_(f) 15.6° C. 36.8° C.25.2° C. 25.0° C. Final vapor conc. c_(f) 13.4 mg/L 43.6 mg/L 23.4 mg/L23.0 mg/L Evap. fraction of  7.1% 98.7% 77.2% 75.2% droplet Finaldroplet radius 2.44 μm 0.60 μm 1.53 μm 1.57 μm R_(df) Time until 2.525ms 2.30 ms 5.18 ms 30.0 ms equilib. τ_(d) Heating energy — — — 36 J/Ldensity

The first example has already been discussed above.

The second example shows that the start temperature would have to bevery high (95° C., probably yielding a safety issue), but the timeneeded to come into equilibrium is still very short (2.30 ms). It isshorter than in the first example, because the diffusion coefficient Dis higher at the higher average temperature of 66° C. The averageheating power during inhalation would be 49.2 W.

The third example appears quite attractive. When supplying air with astart temperature of 4° C. to a personal humidifier operating at halfpower (c_(l)=16 mg/L), then an equilibrium composition of 100% RH air at25° C. with 3 μm diameter droplets is established with a time constantof 5.3 ms. This time constant is longer than in the first example,mainly because the diffusion length (radius R_(occ) of the occupiedvolume) is increased when the number of droplets per volume is reduced.This time constant thus corresponds to an average travelled distance of1.65 cm or a peak distance travelled on the axis of 7.75 cm. Such a“safety distance” between droplet injection and subject's tissue can beeasily established. When combined with a fast thermocouple near theentrance of the tracheal cannula (to be able to switch off the airheating if the nebulizer stops injecting droplets) a safe device can beconstructed. The average heating power during inhalation would be 18.4W. An additional benefit is that the droplet size entering the trachealcannula is diminished by evaporation (5 μm down to 3 μm) so that alarger fraction of droplets is able to reach the deeper airways withouthitting the walls of the trach bend.

In the fourth example, it is assumed that the same situation as in thethird example is desired (T_(f)=25° C.). As a consequence, an energydensity of e_(h)=36 J/L is supplied to the air volume to realize thissituation. The total inhaled volume is V_(inh)=0.5 L and the total timefor inhalation is t_(inh)=1 s. The average heating power duringinhalation is P_(h)=e_(h)*V_(inh)/t_(inh)=18 W. The peak heating poweris 18 W*70[L/min]/30[L/min]=42 W. The time dependence of the heatingpower density p_(h) is assumed to be the same as for thediffusion/conduction terms, i.e., an exponential decrease with timeconstant τ_(d).

Unfortunately, the time constant τ_(d) is becoming very large (30 ms) inthis example. This is a consequence of the fact that the temperaturegradients (which are driving the conduction/diffusion phenomena) are nowmuch smaller than in the third example. The average travelled distanceuntil establishing the equilibrium is now 9.5 cm and the peak distancetravelled on the axis is about 45 cm. These high distances untilequilibrium let this proposition appear as rather impractical for a“personal humidifier.” Of course one could apply a high power density.However, this would then necessarily lead to an overshoot intemperature, because a high temperature gradient close to the dropletsurface is needed to come to the desired short time constant τ_(d).

Returning to FIG. 1, electronic storage 50 comprises electronic storagemedia that electronically stores information. The electronic storagemedia of electronic storage 50 may comprise one or both of systemstorage that is provided integrally (i.e., substantially non-removable)with system 10 and/or removable storage that is removably connectable tosystem 10 via, for example, a port (e.g., a USB port, a firewire port,etc.) or a drive (e.g., a disk drive, etc.). Electronic storage 50 maycomprise one or more of optically readable storage media (e.g., opticaldisks, etc.), magnetically readable storage media (e.g., magnetic tape,magnetic hard drive, floppy drive, etc.), electrical charge-basedstorage media (e.g., EEPROM, RAM, etc.), solid-state storage media(e.g., flash drive, etc.), and/or other electronically readable storagemedia. Electronic storage 50 may store software algorithms, informationdetermined by processor 22, information received via user interface 20,and/or other information that enables system 10 to function properly.Electronic storage 50 may be (in whole or in part) a separate componentwithin system 10, or electronic storage 50 may be provided (in whole orin part) integrally with one or more other components of system 10(e.g., user interface 20, pressure generator 14, processor 22, etc.).

By way of a non-limiting example, electronic storage 50 may beconfigured to store information related to a comfort level of subject 12and corresponding parameters of the pressurized flow of breathable gas.Electronic storage 50 may be configured to store information related toambient weather conditions, a season of the year, and/or otherinformation that corresponds to the comfort level of subject 12,parameters of the pressurized flow of breathable gas, and/or otherinformation.

FIG. 8 illustrates a method 800 for adjusting humidity of a pressurizedflow of breathable gas delivered to the airway of a subject with apressure support system. The pressure support system comprises apressure generator, a nebulizer, a heater, one or more sensors, a userinterface, one or more physical computer processors, a subjectinterface, and/or other components. The operations of method 800presented below are intended to be illustrative. In some embodiments,method 800 may be accomplished with one or more additional operationsnot described, and/or without one or more of the operations discussed.Additionally, the order in which the operations of method 800 areillustrated in FIG. 8 and described below is not intended to belimiting.

In some embodiments, method 800 may be implemented in one or moreprocessing devices (e.g., a digital processor, an analog processor, adigital circuit designed to process information, an analog circuitdesigned to process information, a state machine, and/or othermechanisms for electronically processing information). The one or moreprocessing devices may include one or more devices executing some or allof the operations of method 800 in response to instructions storedelectronically on an electronic storage medium. The one or moreprocessing devices may include one or more devices configured throughhardware, firmware, and/or software to be specifically designed forexecution of one or more of the operations of method 800.

At an operation 800, a pressure generator generates a pressurized flowof breathable gas for delivery to an airway of subject 12. In someembodiments, operation 800 is performed by a pressure generator the sameas or similar to pressure generator 14 (shown in FIG. 1 and describedherein).

At an operation 804, the pressurized flow of breathable gas ishumidified (i.e., moisture is provided to the pressurized flow ofbreathable gas). In some embodiments, operation 804 is performed by anebulizer the same as or similar to nebulizer 16 (shown in FIG. 1 anddescribed herein).

At an operation 806, a volume of the breathable gas is heated beforefluid droplets are provided to the breathable gas (i.e., beforeoperation 804). In some embodiments, operation 906 is performed by aheater the same as or similar to one or more sensors the same as orsimilar to heater 38 (shown in FIGS. 1 and 4 and described herein). Thebreathable gas received by subject 12 exhibits a target temperature andhumidity level at short distance d (mentioned herein) from the nebulizerdue to one or more of a number of the droplets, an average size of thedroplets, a gas flow rate, and/or an amount of heating power.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word “comprising” or “including”does not exclude the presence of elements or steps other than thoselisted in a claim. In a device claim enumerating several means, severalof these means may be embodied by one and the same item of hardware. Theword “a” or “an” preceding an element does not exclude the presence of aplurality of such elements. In any device claim enumerating severalmeans, several of these means may be embodied by one and the same itemof hardware. The mere fact that certain elements are recited in mutuallydifferent dependent claims does not indicate that these elements cannotbe used in combination.

Although the description provided above provides detail for the purposeof illustration based on what is currently considered to be the mostpractical and preferred embodiments, it is to be understood that suchdetail is solely for that purpose and that the disclosure is not limitedto the expressly disclosed embodiments, but, on the contrary, isintended to cover modifications and equivalent arrangements that arewithin the spirit and scope of the appended claims. For example, it isto be understood that the present disclosure contemplates that, to theextent possible, one or more features of any embodiment can be combinedwith one or more features of any other embodiment.

1. A system configured to facilitate humidification of a pressurizedflow of breathable gas delivered to a subject, the system comprising: apressure generator configured to generate a pressurized flow ofbreathable gas for delivery to an airway within a trachea of thesubject; a nebulizer configured to provide fluid droplets to thebreathable gas; a heater configured to heat a volume of the breathablegas before droplets are supplied to the breathable gas; one or morehardware processors configured by machine-readable instructions to:cause the pressure generator to deliver a flow of breathable gas to thesubject; cause the nebulizer to provide the droplets to the breathablegas; and cause the heater to heat a volume of the breathable gas beforethe droplets are supplied to the breathable gas; wherein the breathablegas received by the subject exhibits a target temperature and humiditylevel at short distance d from the nebulizer due to one or more of anumber of the droplets, an average size of the droplets, a gas flowrate, and/or an amount of heating power, wherein the distance d is in arange from 1 cm to 30 cm.
 2. The system of claim 1, further comprising afast temperature sensor located at an entrance leading to the subject tofacilitate controlling operating conditions.
 3. The system of claim 2,wherein the fast temperature sensor is configured to trigger aswitch-off of the heater when a threshold temperature is reached at theentrance leading to the subject indicating that the nebulizer is failingto produce droplets.
 4. The system of claim 1, further comprising atracheal cannula having a bend and being communicatively coupled withthe pressure generator, the tracheal cannula having an inner lumendiameter and the bend of the tracheal cannula having a curvature radius,wherein the tracheal cannula is configured to supply the breathable gasto the airway of the subject, wherein the inner lumen diameter and thecurvature radius facilitate the delivery of the droplets to the tracheaof the subject such that the breathable gas received by the subjectexhibits a target temperature and humidity level, wherein the dropletsare fully evaporated and the droplet size is tuned to demands of thetracheal cannula to reduce impaction.
 5. The system of claim 4, whereinthe inner lumen diameter falls within a range of about 4 mm to about 11mm.
 6. The system of claim 4, wherein the curvature radius falls withina range of about 17 mm to about 25 mm.
 7. (canceled)
 8. The system ofclaim 1, wherein a time-dependent air heating power is modulated andproportional to the flow of breathable gas, wherein there is no heatingduring exhalation.
 9. The system of claim 1, wherein a targettemperature of between about room temperature and 42° C. and a relativehumidity are maintained at an interface to the subject, the relativehumidity being about 100%.
 10. A method for facilitating humidificationof a pressurized flow of gas delivered by a system comprising a pressuregenerator, a nebulizer, a heater, and one or more hardware processors,the method comprising: generating, with the pressure generator, apressurized flow of gas; providing fluid droplets, with the nebulizer,to the pressurized flow of gas; and heating, with the heater, a volumeof the gas before droplets are supplied to the gas; wherein the gasdelivered by the system exhibits a target temperature and humidity levelat short distance d from the nebulizer due to one or more of a number ofthe droplets, an average size of the droplets, a gas flow rate, and/oran amount of heating power, wherein the distance d is in a range from 1cm to 30 cm.
 11. The method of claim 10, the one or more hardwareprocessors are further configured to cause the fast temperature sensorto trigger a switch-off of the heater when a threshold temperature isreached at an interface of the system, indicating that the nebulizer isfailing to produce droplets.
 12. The method of claim 10, wherein gas isdelivered via a tracheal cannula having a bend and being communicativelycoupled with the pressure generator, the tracheal cannula having aninner lumen diameter and the bend of the tracheal cannula having acurvature radius, wherein the inner lumen diameter and the curvatureradius facilitate the delivery of the droplets such that the deliveredgas exhibits a target temperature and humidity level, wherein thedroplets are fully evaporated and the droplet size is tuned to demandsof the tracheal cannula to reduce impaction.
 13. The method of claim 12,wherein the inner lumen diameter falls within a range of about 4 mm toabout 11 mm.
 14. The method of claim 12, wherein the curvature radiusfalls within a range of about 17 mm to about 25 mm.
 15. A system forfacilitating humidification of a pressurized flow of breathable gasdelivered to a subject, the system comprising: means for generating apressurized flow of breathable gas for delivery to an airway within atrachea of the subject; means for providing fluid droplets to thepressurized flow of breathable gas; and means for heating a volume ofthe breathable gas before the droplets are supplied to the breathablegas; wherein the breathable gas received by the subject exhibits atarget temperature and humidity level at short distance d from thenebulizer due to one or more of a number of the droplets, an averagesize of the droplets, a gas flow rate, and/or an amount of heatingpower, wherein the distance d is in a range from 1 cm to 30 cm.
 16. Thesystem of claim 15, wherein the means for providing fluid droplets is avibrating mesh nebulizer configured to cause a mist of water droplets ofa defined diameter to be generated.
 17. The system of claim 15, furthercomprising a means for facilitating controlling operating conditions,the means for facilitating controlling operating conditions located atan entrance of the means for facilitating the delivery of fluid dropletsto the trachea of the subject.
 18. The system of claim 15, wherein themeans for facilitating controlling operating conditions is configured toa switch-off of the means for heating if the means for supplying fluiddroplets to the pressurized flow of breathable gas fails to producedroplets.
 19. (canceled)